To identify cellular genes required for optimal HIV-1 infection, or involved in HIV-1 pathogenesis. - To study the mechanism by which intrathymic HIV-1 infection affects the development of different T cell subsets. - To understand how HIV-1 infection leads to high levels of programmed cell in both CD4 and CD8 cells. - To apply the knowledge gained towards development of anti-viral therapy which target both viral and cellular genes. (2) Experimental approach: - Scid/Hu mice were infected intrathymically with primary isolate of HIV. Thymocytes were separated into various subsets by 3 color stainings and the presence of proviral DNA was determined by quantitative PCR. - Rabbit Igs specific for the CXCR4 and CCR5 extracellular domains were produced and tested for their ability to stain primary human cells and to block viral fusion and infection. - Study coreceptor expression and function on human thymocyte subpoulations and (3) Major Findings: - The Hu/Scid model demonstrated that in the infected thymus, that CD3hiCD8+ mature cells are also infected with the virus. The HIV-1 infected CD3hiCD8+ thymocytes also express viral mRNA. These cells are not found in the periphery of infected mice, suggesting intrathymic death. Experiments suggested that the infection may occur during the development of CD4+CD8+ infected cell into single positive CD4 and CD8 cells. The study provides new mechanism for the reported depletion of naive CD8 cells in the periphery of infected individuals, that may contribute to their inability to handle opportunistic infections. Manuscript by Shirley Lee et al. was published in J.Virol. 71:6671-6676 Studies with human thymocyte subpopulations from infants, revealed very high expression of the CXCR4 coreceptor on immature thymocytes, including CD34+ intrathymic precursors. Thymocytes responded to the chemokine SDF1 by chemotaxis and Ca++ mobilization. They fused readily with T-tropic HIV envelopes and the fusion was blocked by our rabbit anti-CXCR4 IgG. In addition, we have evidence that another chemokine receptor (I-309R) is expressed in human thymocytes and provides co-recptor function for infection with T-tropic and M-trpic strains. These data explain the exquisite sensitivity of neonatal thymuses to infection with T-tropic HIV strains that often result in sever thymic depletion. Manuscript by Zaitseva et al. is in press in J. Immunol. (September 1 1998).